QUARTZ DEFORMATION IN A SYNTECTONIC PLUTO N EMPLACED DURING THE LATE CARBONIFEROUS EXTENSION IN THE FRENCH MASSIF-CENTRAL (THE CHAMBLES LEUKOGRANITE, VELAY MASSIF)

Mapping and petrostructural studies of the Chambles leucogranite (W of St-Etienne) allow reconstruction of the pluton shape. This intrusion emplaced during the Late Carboniferous crustal thinning. This pluton, rooted to the SW and overturned to the NE, shows a mylonitic facies to the East and a weakly deformed facies in the remaining granite. The p etrofabric analysis of quartz shows that in the mylonite, the deformat ion is due to a low temperature translation glide whilst in the weakly deformed facies, high temperature solid-state diffusion is prepondera nt.